1. Field of Invention
The present invention relates generally to stereoscopic viewing devices enabling a person to perceive three-dimensional images. Specifically, the invention can be used to upgrade a regular computer monitor or TV set to a powerful and affordable tool for visualizing three-dimensional graphics.
2. Description of Prior Art
The basic principle underlying all stereoscopic viewing devices is to arrange for the viewer's left and right eyes to see two separate images, differing in such a way that the resulting mental image is three-dimensional. A common feature of the multitude of such devices developed to date is lack of commercial success on the broad consumer market.
Methods where both images are printed interleaved, and the viewer is required to focus his eyes beyond them in order for them to be perceived as a single three-dimensional image, can cause eye-strain. Furthermore, some people are unable to use them at all, despite trying for several minutes.
Methods based on color light (known as anaglyphic), such as the familiar red and green viewing glasses used in experimental TV-broadcasts, cannot accurately reproduce color images and generally yield imperfect pictures because the filters fail to eliminate the complementary color completely.
Methods based on polarized light, such as U.S. Pat. No. 5,007,715 (Verhulst), tend to be prohibitively expensive for the home user, since they cannot be used with regular computer or TV screens, which emit unpolarized light.
Prohibitive costs also hamper methods involving
rapidly moving parts, such as U.S. Pat. No. 366,823 (Ferry), PA0 a screen deformed in a lenticular fashion so that the left and right eyes see mutually exclusive parts of it, such as U.S. Pat. No. 4,959,641, or PA0 two separate screens, either in combinations with mirrors as in U.S. Pat. No. 5,023,912 (Sakariassen) or U.S. Pat. No. 4,743,964 (Allard et al.), or miniaturized and mounted on the viewer's head directly in front of the individual eyes as in U.S. Pat. No. 4,933,755 (Dahl et al.). PA0 U.S. Pat. No. 4,674,845X (allowing 3D viewing through a microscope), PA0 U.S. Pat. No. 4,457,584 (primarily designed to be head-mounted and used at cinemas) and PA0 U.S. Pat. No. 5,101,269 (designed to view pairs of photographic slides and prints stereographically). PA0 a) The perceived image should still upper three-dimensional and undistorted if the viewer rotates his head slightly, as is inevitable during an extended period of use. This rules out mirrors mounted on the viewer's head. PA0 b) When the devices is used with a computer monitor, the viewer should not be forced to bend down and hold his head straight in front of the screen, which would be required by a mirror arrangement such as U.S. Pat. No. 4,457,584 (Pryor) or U.S. Pat. No. 4,568,970 (Rockstead). Rather, an ergonomically sound posture should be allowed, where the user can sit fairly upright at a desk and view at a downward-slanting angle like during normal computer work. PA0 c) The resulting three-dimensional image should have a shape similar to a normal screen, i.e. slightly broader than it is wide. To achieve this, the left and right halves of the screen would have to be not only superimposed, but also rotated by ninety degrees. No previously designed devices do this. PA0 d) The device should be usable for a variety of screen sizes without requiring readjustment of its mirrors.
Time-divided viewing methods such as U.S. Pat. No. 4,907,860 (Noble), where liquid crystals alternately block out the left and right eyes, can cause flickering discomfort since at any time, in eye is viewing nothing. Also, at least half of the light is absorbed by the polarizer even when it is transparent, rendering the image rather dark.
The cheapest devices to manufacture are those using no other optical components than mirrors. An additional advantage is that these suffer from none of the reductions in viewing quality discussed above: their is full color, no flicker, virtually no loss of light, etc. Representative devices of this type are
Unfortunately, none of these devices are suitable for superimposing the left and right halves of a standard computer monitor or TV screen in a way which is practical and allows the viewer to sit in an ergonomically acceptable position. Ideally, such a device should satisfy the following requirements: